diff --git a/src/define.sh b/src/define.sh
index a85cd41c..683b1577 100644
--- a/src/define.sh
+++ b/src/define.sh
@@ -417,6 +417,7 @@ printVersion() {
     "win9x"* ) desc="Windows ME" ;;
     "win98"* ) desc="Windows 98" ;;
     "win95"* ) desc="Windows 95" ;;
+    "winnt4"* ) desc="Windows NT 4" ;;
     "win2k"* ) desc="Windows 2000" ;;
     "winvista"* ) desc="Windows Vista" ;;
     "win2019-hv"* ) desc="Hyper-V Server" ;;
diff --git a/src/image.sh b/src/image.sh
index 48ccd535..aa27f526 100644
--- a/src/image.sh
+++ b/src/image.sh
@@ -1753,13 +1753,6 @@ buildImage() {
     error "Failed to locate file \"$ETFS\" in ISO image!" && return 1
   fi
 
-  if [[ "${BOOT_MODE,,}" == "windows_legacy" &&
-    "${DETECTED,,}" != "win9"* &&
-    -z "${BOOT_LOAD_SIZE:-}" ]]; then
-    error "Failed to determine the boot image load size!"
-    return 1
-  fi
-
   if ! size=$(du -b --max-depth=0 "$dir" | cut -f1); then
     error "Failed to calculate the size of directory \"$dir\"!"
     return 1
@@ -1767,6 +1760,13 @@ buildImage() {
 
   checkFreeSpace "$TMP" "$size" || return 1
 
+  if [[ "${BOOT_MODE,,}" == "windows_legacy" ]] && [ -z "${BOOT_LOAD_SIZE:-}" ]; then
+    if [[ "${DETECTED,,}" != "win9"* && "${DETECTED,,}" != "winnt4" ]]; then
+      error "Failed to determine the boot image load size!"
+      return 1
+    fi
+  fi
+
   /run/progress.sh "$out" "$size" "$msg ([P])..." &
 
   local -a args=(
@@ -1816,7 +1816,7 @@ buildImage() {
           "${name_args[@]}"
         ) ;;
 
-      "win9"* )
+      "win9"* | "winnt4" )
 
         args+=(
           -J
diff --git a/src/install.sh b/src/install.sh
index e78a5694..1262e71d 100644
--- a/src/install.sh
+++ b/src/install.sh
@@ -923,8 +923,10 @@ prepareImage() {
   desc=$(printVariant "$DETECTED" "$DETECTED")
 
   # Legacy rebuilt media must retain the source ISO's El Torito boot-load size.
-  if [[ "${BOOT_MODE,,}" == "windows_legacy" && "${DETECTED,,}" != "win9"* ]]; then
-    getBootLoadSize "$iso" "$dir" "$desc" || return 1
+  if [[ "${BOOT_MODE,,}" == "windows_legacy" ]]; then
+    if [[ "${DETECTED,,}" != "win9"* && "${DETECTED,,}" != "winnt4" ]]; then
+      getBootLoadSize "$iso" "$dir" "$desc" || return 1
+    fi
   fi
 
   supportsXML "$DETECTED" || return 0
@@ -1586,7 +1588,7 @@ setMachine() {
 
   case "${id,,}" in
 
-    "win9"* )
+    "win9"* | "winnt4" )
 
       writeState "usb" "N" || return 1
       writeState "net" "pcnet" || return 1
@@ -1626,7 +1628,7 @@ setMachine() {
 
   case "${id,,}" in
 
-    "win9"* | "win2k"* | *"x86"* | "reactos" )
+    "win9"* | "winnt4" | "win2k"* | *"x86"* | "reactos" )
 
       # Legacy 32-bit Windows may enter an incompatible PAE/DEP path when the
       # NX flag is exposed, causing installation failures or repeated resets.
@@ -1637,7 +1639,7 @@ setMachine() {
 
   case "${id,,}" in
 
-    "win9"* | "win2k"* | "winxp"* | "win2003"* | \
+    "win9"* | "winnt4" | "win2k"* | "winxp"* | "win2003"* | \
     "winvistax86"* | "win7x86"* | "reactos" )
 
       if isQ35 "$MACHINE"; then